I don't know how to tell if he's a good coach or not. He hasn't been successful anywhere, to my knowledge, but the extent of my awareness of him only goes back to when he took over Sarkesian's finely tuned machine, followed by several mediocre to poor head coaching performances.

You've got it backwards. Kiffin set that up and Sarkisian moved in after Kiffin went to the Raiders. Dude's a good OC, just not a good head coach.